Process and device for boost control

ABSTRACT

An arrangement for boost control either has a pressure sensor and a differential-pressure sensor, the pressure sensor being connected to one of two suction paths of an internal combustion engine and the differential-pressure sensor being located between the two suction paths, or the device possesses a single pressure sensor 18 which is switched alternately to the first suction path 11.1 and to the second suction path 11.2 by means of a change-over valve 24. 
     These arrangements and the associated methods make it possible to control to the same predetermined pressure in the two suction paths with a high degree of accuracy. This is because there is no possibility of a systematic error which, in previous arrangements and methods, arose from the fact that the pressures in the two suction paths were measured by separate pressure sensors. However, different pressure sensors in a simple version indicate different values at the same pressures.

FIELD OF THE INVENTION

The invention relates to a method and an arrangement for controlling theboost pressure on an internal combustion engine with a first and asecond suction path, each having suction pressures which are controlled.

BACKGROUND OF THE INVENTION

There is a known arrangement for boost control, having two pressuresensors which each measure the suction-path pressure in one of the twosuction paths. These measured suction-path pressures are each comparedwith a desired value, and one of two means of controlling determines aduty factor for a bypass valve on each of the two supercharging turbinesfrom the respective control deviation values.

With the known arrangement, therefore, there are different suction-pathpressures when the two pressure sensors do not work in an identical way,which happens frequently.

SUMMARY OF THE INVENTION

The object on which the invention is based is to provide a method forboost control, by means of which the boost pressures in two suctionpaths can each be regulated to the same value with a high degree ofaccuracy. A further object on which the invention is based is to providean arrangement for carrying out such a method.

The invention relates to a method for boost control in an internalcombustion engine having a first and a second suction path with thesuction pressures of each path being controlled. According to a firstembodiment of the method, the boost pressure in the first suction pathis measured and this boost pressure is regulated to a desired value. Thedifferential pressure between the boost pressures in the first andsecond suction paths is measured and the boost pressure in the secondsuction path is regulated to the desired value by taking into accountthe boost pressure in the first suction path and the differentialpressure.

In a second embodiment of the method of the invention, the boostpressures in the first and second suction paths are measured alternatelyby switching over the pressures to a single pressure sensor. The controlvalue determined for one suction path is maintained, while the boostpressure for the other suction path is measured and controlled.

In the arrangement according to the invention, a pressure sensor isconnected only to one suction path. Additionally, however, there is adifferential-pressure sensor between the two suction paths. It ispossible by means of this arrangement to carry out a method according towhich the suction pressure in that suction path, to which the pressuresensor is connected, is controlled directly by means of the measuredpressure signal, while the pressure in the other suction path iscontrolled by means of the pressure signal from the other suction pathand the differential pressure. This arrangement and the associatedmethod do not place high demands on the accuracy of the pressure sensorand of the differential-pressure sensor. It is merely necessary toensure that, when the differential pressure is 0, thedifferential-pressure sensor indicates this differential pressure 0correctly.

In another embodiment of the arrangement according to the invention,there is only a single pressure sensor which can be connectedalternately to the two suction paths. Thus, since the same pressuresensor is used for pressure measurement in both suction paths, identicalsuction-path pressures can be set easily, irrespective of the accuracyof the pressure sensor. The method with the arrangement just mentionedworks in such a way that, during the time when the pressure signal forone suction path is being measured, the pressure signal for the othersuction path is maintained, so that it is available for the control.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail below by means of the embodimentsillustrated by figures. Of these:

FIG. 1 shows an arrangement for boost control with a pressure sensor anda differential-pressure sensor; and

FIG. 2 shows an arrangement for boost control with a single pressuresensor which can be fitted alternately to two suction paths.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The boost-control arrangement according to FIG. 1 is used there on aV-engine with 8 cylinders which has two banks 10.1 and 10.2 of 4cylinders each. A first supercharger 12.1 is arranged in the suctiontract 11.1 of the first bank 10.1, while in the associated exhaust-gastract 13.1 there is a first turbine 14.1 which is driven by the exhaustgas and which thereby drives the supercharger 12.1. The drivingconnection between the supercharger 12.1 and the turbine 14.1 isrepresented by a solid line. A first timing valve 16.1 drivable by meansof the first timing control 17.1 is arranged in a bypass line 15.1 tothe first turbine 14.1. The bypass throughflow rate and consequently therotational speed of the turbine 14.1 and thereby, in turn, the boostpressure provided by the first supercharger 12.1 can be set byactivating the timing valve 16.1.

Components corresponding to those on the first bank 10.1 are present onthe second bank 10.2. Corresponding reference symbols bear theadditional designation "0.2" instead of "0.1".

The arrangement for boost control has a pressure sensor 18, adifferential-pressure sensor 19, a desired-value transmitter 20, a firstmeans of control 21.1 and a second means of control 21.2. Moreover, anaddition unit 22 as well as a first subtraction unit 23.1 and a secondsubtraction unit 23.2 are provided. The pressure sensor 18 is connectedto the first suction tract 11.1, and the differential-pressure sensor 19connects the first suction path 11.1 to the second suction path 11.2.

This arrangement functions as follows.

The signal emitted by the pressure sensor 18, namely a voltage signalUPS1, is supplied to the first subtraction unit 23.1. There, this signalis subtracted from a desired voltage UP₋₋ des. The control deviation UPlis supplied to the first means of control 21.1 which emits in the usualway a timing signal to the first timing control 17.1 as a function ofthe control deviation.

To that extent, the functioning of the arrangement illustrated in no waydiffers from the arrangement known from the state of the art.

In the arrangement according to the state of the art, the boost controlfor the second bank works in a completely identical way to the boostcontrol for the first bank, that is, there is also a second pressuresensor connected to the second suction path. However, this is not truefor the arrangement illustrated. In particular, a voltage measured by asecond pressure sensor is not supplied to the second subtraction unit23.2, but instead the subtraction unit 23.2 receives a signal whichcorresponds to the sum of the pressure signal UPS1 from the pressuresensor 18 and of the differential-pressure signal UΔP from thedifferential-pressure sensor 19. The sum of these two signals is formedin the addition unit 22. The differential-pressure sensor 19 isconnected in such a way that, when the pressure in the second suctionpath 11.2 is higher than in the first suction path 11.1, it emits asignal with a sign corresponding to the sign of the signal UPS1 from thepressure sensor 18. Otherwise, the control of the boost pressure for thesecond bank 10.2 takes place exactly according to the above-describedcontrol for the first bank 10.1. The difference, therefore, is only thatthe actual values for the control are formed differently.

For the calibration of the arrangement, it is merely necessary to ensurethat the differential-pressure sensor 19 emits a signal of the value 0at the pressure difference 0. Moreover, the demands of accuracy placedon the pressure sensor 18 and the differential-pressure sensor 19 arenot high, since it is only important to set the same pressure in each ofthe two suction paths 11.1 and 11.2, this being guaranteed when thedifferential-pressure sensor 19 then transmits the value 0.

An arrangement is explained with reference to FIG. 2 which can beproduced even more cost-effectively than the arrangement according toFIG. 1, specifically because only a single pressure sensor 18 is usedinstead of a pressure sensor 18 and a differential-pressure sensor 19.In the arrangement according to FIG. 2, not only thedifferential-pressure sensor 19, but also the addition unit 22 isomitted. Instead, there are as additional functional parts a change-overvalve 24 and a clock generator 25 which activates a firstsensing/holding circuit 26.1, a second sensing/holding circuit 26.2, asignal switch 27 and a valve change-over switch 28. All the otherfunctional parts correspond exactly to those of the arrangementaccording to FIG. 1.

The change-over valve 24 has two switch positions. In the first switchposition shown, it connects the first suction path 11.1 to the pressuresensor 18. Correspondingly, in its second position, it connects thesecond suction path 11.2 to the pressure sensor 18. The valve can bechanged over pneumatically between the two positions, this taking placeby means of the valve switch 28 according to the timing predetermined bythe timing generator 25. In the example, the timing frequency is 10 Hz.Whenever the pressure sensor 18 has just been connected to the firstsuction path 11.1, the signal switch 27 switches the output signal USP1from the pressure sensor 18 to the first sensing/holding circuit 26.1 inresponse to the timing signal from the timing generator 25. From thefirst sensing/holding circuit 26.1, output signal USP1 arrives at thefirst subtraction unit 23.1. There, a difference is formed again toobtain a desired value UP₋₋ des which is emitted by the desired-valuetransmitter 20 as a function of the values of the engine speed n and aload-dependent parameter L, for example the throttle-flap angle. Thefurther control cycle takes place in the way described above withreference to FIG. 1.

In contrast, if the pressure sensor 18 was connected to the secondsuction path 11.2 by means of the timing signal from the timinggenerator 25, the signal switch 27 correspondingly switches the outputsignal USP2 from the pressure sensor 18 to the second sensing/holdingcircuit 26.2 and from there to the second subtraction unit 23.2. Whatwas said above applies accordingly to the further control.

In practice, as many of the functional groups described as possible areimplemented by the functioning of a microcomputer. These areparticularly the desired-value transmitter 20 which is then designed,for example, as a memory, the two means of control 21.1 and 21.2, thesubtraction units 23.1 and 23.2, the addition unit 22 and thesensing/holding circuits 26.1 and 26.2. The sensing/holding functions donot necessarily have to be at the illustrated point along the signalpath. They can also perform their function, for example, at the outputsof the means of control. A microcomputer senses, for example, thepressure sensor 18 at predetermined time intervals whenever the latterhas just been switched to one of the two suction paths. The measuredvalue is used to calculate a new actuating value for the associatedcontrol circuit. The actuating value in the other control circuit ismaintained and emitted to the associated timing control until a newactuating value is calculated for this control circuit too.

The above-described functional cycles correspond to preferredembodiments. However, the functional cycles described in detail are notessential to the invention, but it is crucial that the pressure controlin the two suction paths should not be carried out by means of twoseparate pressure sensors, but either by means of a pressure sensor anda differential-pressure sensor or by means of a single pressure sensorwhich is switched alternately to the two suction paths.

What is claimed is:
 1. A method for boost control in an internalcombustion engine having a first suction path communicating with a firstsupercharger and a second suction path communicating with a secondsupercharger wherein the respective suction pressures are controlled,the method comprising the steps of:measuring the boost pressure in thefirst suction path and regulating this boost pressure to a desiredvalue; and, measuring the differential pressure between the boostpressures in the first and second suction paths and regulating the boostpressure in the second suction path to the desired value by utilizingboth said boost pressure in the first suction path and said differentialpressure.
 2. A method for boost control in an internal combustion enginehaving a first suction path communicating with a first supercharger anda second suction path communicating with a second supercharger, themethod comprising the steps of:measuring the boost pressures in thesuction paths and controlling the measured boost pressures to a samedesired value; alternately measuring the boost pressures in the firstand second suction paths by switching over the pressures in said suctionpaths to a single pressure sensor; and, maintaining the control valuedetermined for one of the suction paths while measuring and controllingthe boost pressure for the other one of the suction paths.
 3. Anarrangement for providing boost control in an internal combustion enginehaving a first suction path communicating with a first supercharger anda second suction path communicating with a second supercharger whereinrespective boost pressures are present during operation of the engine,the arrangement comprising:a pressure sensor connected to one of saidsuction paths for providing a first signal indicative of the pressure insaid one suction path; a differential pressure sensor connected betweensaid suction paths for providing a second signal indicative of thedifference pressure between said paths; first control means forcontrolling the boost pressure in said first suction path to a desiredvalue; second control means for controlling the boost pressure in saidsecond suction path to said desired value; said first control meansbeing connected to said pressure sensor and including means forprocessing said first signal as an actual value; and, said secondcontrol means being connected to each of said sensors and includingmeans for processing said first and second signals as actual values. 4.An arrangement for providing boost control in an internal combustionengine having a first suction path communicating with a firstsupercharger and a second suction path communicating with a secondsupercharger wherein respective boost pressures are present duringoperation of the engine, the arrangement comprising:a pressure measuringapparatus for measuring the boost pressure in each of the suction paths,the pressure measuring apparatus including a single pressure sensor forproviding a signal indicative of the pressure measured; and, switchovermeans for alternately connecting said pressure sensor to said suctionpaths for alternately providing first and second signals indicative ofthe respective pressures measured in corresponding ones of said suctionpaths; first control means for controlling the boost pressure in saidfirst suction path to a desired value; second control means forcontrolling the boost pressure in said second suction path to saiddesired value; and, each of said control means including: means forholding a control variable for the suction path corresponding theretowhile said pressure sensor measures the pressure in the suction pathcorresponding to the control means.